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Summary: Methods | Protected Methods | Inherited Methods

# VelocityTracker

`public final class VelocityTracker`
`extends Object` ``

java.lang.Object
↳ | android.view.VelocityTracker

Helper for tracking the velocity of touch events, for implementing flinging and other such gestures. Use `obtain()` to retrieve a new instance of the class when you are going to begin tracking. Put the motion events you receive into it with `addMovement(android.view.MotionEvent)`. When you want to determine the velocity call `computeCurrentVelocity(int)` and then call `getXVelocity(int)` and `getYVelocity(int)` to retrieve the velocity for each pointer id.

## Summary

### Public methods
`void` | `addMovement(MotionEvent event)` Add a user's movement to the tracker.
`void` | `clear()` Reset the velocity tracker back to its initial state.
`void` | `computeCurrentVelocity(int units)` Equivalent to invoking `computeCurrentVelocity(int, float)` with a maximum velocity of Float.MAX_VALUE.
`void` | `computeCurrentVelocity(int units, float maxVelocity)` Compute the current velocity based on the points that have been collected.
`float` | `getXVelocity(int id)` Retrieve the last computed X velocity.
`float` | `getXVelocity()` Retrieve the last computed X velocity.
`float` | `getYVelocity()` Retrieve the last computed Y velocity.
`float` | `getYVelocity(int id)` Retrieve the last computed Y velocity.
`static VelocityTracker` | `obtain()` Retrieve a new VelocityTracker object to watch the velocity of a motion.
`void` | `recycle()` Return a VelocityTracker object back to be re-used by others.

### Protected methods
`void` | `finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

### Inherited methods
From class `java.lang.Object`
`Object` | `clone()` Creates and returns a copy of this object.
`boolean` | `equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void` | `finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>` | `getClass()` Returns the runtime class of this `Object`.
`int` | `hashCode()` Returns a hash code value for the object.
`final void` | `notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void` | `notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String` | `toString()` Returns a string representation of the object.
`final void` | `wait(long timeout, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void` | `wait(long timeout)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void` | `wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.

## Public methods

### addMovement

    public void addMovement (MotionEvent event)

Add a user's movement to the tracker. You should call this for the initial `MotionEvent#ACTION_DOWN`, the following `MotionEvent#ACTION_MOVE` events that you receive, and the final `MotionEvent#ACTION_UP`. You can, however, call this for whichever events you desire.

Parameters
`event` | `MotionEvent`: The MotionEvent you received and would like to track.

### clear

    public void clear ()

Reset the velocity tracker back to its initial state.

### computeCurrentVelocity

    public void computeCurrentVelocity (int units)

Equivalent to invoking `computeCurrentVelocity(int, float)` with a maximum velocity of Float.MAX_VALUE.

Parameters
`units` | `int`

See also:

- `computeCurrentVelocity(int, float)`

### computeCurrentVelocity

    public void computeCurrentVelocity (int units,
                    float maxVelocity)

Compute the current velocity based on the points that have been collected. Only call this when you actually want to retrieve velocity information, as it is relatively expensive. You can then retrieve the velocity with `getXVelocity()` and `getYVelocity()`.

Parameters
`units` | `int`: The units you would like the velocity in. A value of 1 provides pixels per millisecond, 1000 provides pixels per second, etc.
`maxVelocity` | `float`: The maximum velocity that can be computed by this method. This value must be declared in the same unit as the units parameter. This value must be positive.

### getXVelocity

    public float getXVelocity (int id)

Retrieve the last computed X velocity. You must first call `computeCurrentVelocity(int)` before calling this function.

Parameters
`id` | `int`: Which pointer's velocity to return.

Returns
`float` | The previously computed X velocity.

### getXVelocity

    public float getXVelocity ()

Retrieve the last computed X velocity. You must first call `computeCurrentVelocity(int)` before calling this function.

Returns
`float` | The previously computed X velocity.

### getYVelocity

    public float getYVelocity ()

Retrieve the last computed Y velocity. You must first call `computeCurrentVelocity(int)` before calling this function.

Returns
`float` | The previously computed Y velocity.

### getYVelocity

    public float getYVelocity (int id)

Retrieve the last computed Y velocity. You must first call `computeCurrentVelocity(int)` before calling this function.

Parameters
`id` | `int`: Which pointer's velocity to return.

Returns
`float` | The previously computed Y velocity.

### obtain

    public static VelocityTracker obtain ()

Retrieve a new VelocityTracker object to watch the velocity of a motion. Be sure to call `recycle()` when done. You should generally only maintain an active object while tracking a movement, so that the VelocityTracker can be re-used elsewhere.

Returns
`VelocityTracker` | Returns a new VelocityTracker.

### recycle

    public void recycle ()

Return a VelocityTracker object back to be re-used by others. You must not touch the object after calling this function.

## Protected methods

### finalize

    protected void finalize ()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. A subclass overrides the `finalize` method to dispose of system resources or to perform other cleanup.

The general contract of `finalize` is that it is invoked if and when the Java™ virtual machine has determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, except as a result of an action taken by the finalization of some other object or class which is ready to be finalized. The `finalize` method may take any action, including making this object available again to other threads; the usual purpose of `finalize`, however, is to perform cleanup actions before the object is irrevocably discarded. For example, the finalize method for an object that represents an input/output connection might perform explicit I/O transactions to break the connection before the object is permanently discarded.

The `finalize` method of class `Object` performs no special action; it simply returns normally. Subclasses of `Object` may override this definition.

The Java programming language does not guarantee which thread will invoke the `finalize` method for any given object. It is guaranteed, however, that the thread that invokes finalize will not be holding any user-visible synchronization locks when finalize is invoked. If an uncaught exception is thrown by the finalize method, the exception is ignored and finalization of that object terminates.

After the `finalize` method has been invoked for an object, no further action is taken until the Java virtual machine has again determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, including possible actions by other objects or classes which are ready to be finalized, at which point the object may be discarded.

The `finalize` method is never invoked more than once by a Java virtual machine for any given object.

Any exception thrown by the `finalize` method causes the finalization of this object to be halted, but is otherwise ignored.

Throws
`Throwable` |

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